Examples of general rubber-reinforced thermoplastic resin comprise ABS, ASA, MBS, and AIM resins. These resins are similar in that a rubber polymer of 0° C. or less is used as a core and a shell selected considering compatibility with a matrix resin is formed through graft polymerization.
For example, in order to secure impact resistance upon preparation of an ABS resin, a large-particle-size rubber polymer having a particle size of 3000 Å is used. In this case, the large-particle-size rubber polymer may be prepared by enlarging a small-particle-size rubber polymer having a particle size of 2000 Å or less, or by directly emulsion-polymerizing a large-particle-size rubber polymer having a particle size of 3000 Å or more. In this case, a rubber latex having a large particle size of 3000 Å or more obtained though the direct emulsion polymerization has narrow particle size distribution and low gel content, and thus having advantageous impact resistance. However, the rubber latex requires a polymerization time of 20 hours or more, and reaction time increases and transition ratio decreases with increasing particle size.
While, a small-particle-size rubber polymer having a particle size of 2000 Å or less has advantageous productivity in that the small-particle-size rubber polymer may be generally prepared within a short time of 15 to 20 hours. When a large-particle-size rubber latex having a particle size of 3000 Å or more is prepared by enlarging the small-particle-size rubber polymer, it is relatively easy control to particle sizes and broad particle size distribution is exhibited. When small-sized particles are present in broad particle size distribution, surface gloss and visibility of a resin are advantageously enhanced. Conventionally, a small-particle-size rubber polymer latex is prepared by simultaneously or separately inputting a butadiene monomer and within a relatively short time of 15 to 20 hours. However, heat from rapid heat reaction generated in this case is cooled with an ammonia refrigerant or low-temperature water using a coil-type cooler in the outside or inside of a reactor. As such, rapid heat reaction occurring after simultaneously and separately inputting of butadiene monomer causes non-uniformity of latex particles and a solid content, whereby continuous long-term operation is hindered and it is difficult to additionally reduce reaction time due to ineffective reaction heat distribution.
In addition, ABS based rubber-reinforced resins are conventionally prepared as a rubber-reinforced resin through emulsion polymerization, and, after preparing into a powder by coagulating/drying the rubber-reinforced resin, the powder-type rubber-reinforced resin is conventionally pelletized a first process step by inputting the same with a matrix resin such as styrene-acrylonitrile and/or polycarbonate to an extruder. In this case, a drying process is generally carried out such that a rubber-reinforced resin having a moisture content of less than 1% is input to an extruder.
In some cases, a first processing step, in which, after dehydrating without drying, a powder having a moisture content of approximately 30% is continuously kneaded with the matrix resin in an extruder, is carried out. However, a high moisture content leads to property deviation and productivity reduction.
Therefore, when a powder comprising moisture is input to an extruder without a dying process, minimizing a moisture content may be an important factor in maintaining productivity and quality.
In addition, since a centrifugal dehydrator conventionally used to reduce moisture content has limitations, a compression-type dehydrator may be used. However, a high-temperature and high-pressure processing process required in a compression-type dehydration process may lead to change of thermal stability and resin deformation.